Over 50 million Americans have cardiovascular problems, and many other countries face high and increasing rates of cardiovascular disease. It is the number one cause of death and disability in the United States and most European countries. By the time that heart problems are detected, the underlying cause, atherosclerosis, is usually quite advanced, having progressed for decades.
Atherosclerosis is a polygenic complex disease of mammals characterized by the deposits or plaques of lipids and other blood derivatives in the arterial walls (aorta, coronary arteries, and carotid). These plaques can be calcified to a greater or lesser extent according to the progression of the process. They are also associated with the accumulation of fatty deposits consisting mainly of cholesterol esters in the arteries. Cholesterol accumulates in the foam cells of the arterial wall, thereby narrowing the lumen and decreasing the flow of blood. This is accompanied by a thickening of the arterial wall, with hypertrophy of the smooth muscle, the appearance of foam cells and the accumulation of the fibrous tissue. Hypercholesterolemia can therefore result in very serious cardiovascular pathologies such as infarction, peripheral vascular disease, stroke, sudden death, cardiac decompensation, cerebral vascular accidents and the like.
The cholesterol is carried in the blood by various lipoproteins including the very low-density lipoprotein (VLDL), the low-density lipoproteins (LDL) and the high-density lipoproteins (HDL). The VLDL is synthesized in the liver and is converted to LDL in the blood, which makes it possible to supply the peripheral tissues with cholesterol. In contrast, the HDL captures cholesterol molecules from the peripheral tissues and transports them to the liver where they are converted to bile acids and excreted. The development of atherosclerosis and the risk of coronary heart disease (CHD) inversely correlate to the levels of HDL in the serum. Gordon et al. (1989) N. Engl. J. Med. 321: 1311; Goldbourt et al. (1997) Thromb Vasc. Biol. 17: 107. Low HDL cholesterols often occur in the context of central obesity, diabetes and other features of the metabolic syndrome. Goldbourt et al., supra. It has been suggested that low HDL cholesterol levels are associated with an increased risk of CHD, while high concentrations of HDL have a protective effect against the development of premature atherosclerosis. Gordon et al. (1986) Circulation 74: 1217. Studies demonstrated that the risk for developing clinical atherosclerosis in men drops 2-3% with every 1 mg/dL increase in the concentration of HDL in plasma. Gordon et al. (1989) N. Engl. J. Med. 321: 1311. It has been established that concentrations of LDL cholesterol can be reduced by treatment with statins, inhibitors of the cholesterols biosynthesis enzyme 3-hydroxyl-3-methylglutary Coenzyme A reductase and thereby this treatment has been used as a successful approach for reducing the risk for atherosclerosis where the primary indication is high LDL level. However, it remains unclear whether statins are beneficial for patients whose primary lipid abnormality is low HDL cholesterol.
Lecithin-cholesterol acyltransferase (LCAT) is an enzyme which catalyses the esterification of free cholesterol by the transfer of an acyl group from phosphatidylcholine onto 3-hydroxyl group of the cholesterol, forming cholesteryl ester and lysophosphatidylcholine. McLean et al. (1986) Proc. Natl. Acad. Sci. 83: 2335 and McLean et al. (1986) Nucleic Acids Res. 14(23): 9397. LCAT is synthesized in the liver and secreted into the plasma, where it is combined with HDL, called anti-atherogenic lipoproteins. These HDL particles have the capacity to accept the excess cholesterol, which is then esterified by LCAT in the HDL particles. The cholesteryl ester molecules in the HDL particles are either transported to the liver directly through SR-BI receptor, or transferred to apoB-containing lipoproteins, including very low density lipoproteins (VLDL) and LDL, mediated by CETP, and then transported to the liver through LDL-receptor pathway. This mechanism, called reverse cholesterol transport (Glomset (1968) J. Lipid Res. 9:155), allows the removal of excess cholesterol from the body, and therefore is involved in the prevention of atherogenesis. LCAT plays a key role in this process by creating a gradient of free cholesterol between the plasma membranes and the circulating lipoproteins.
This invention provides modified LCAT proteins with increased enzymatic activity and/or stability and methods for treatment of coronary heart disease, atherosclerosis, inflammatory disorders and disorders associated with thrombosis using these modified LCAT proteins.